1. Field of the Invention
The present invention relates to an image pickup apparatus that can obtain an image having a high resolution.
2. Related Background Art
In a conventional image pickup apparatus for generating an image signal, object light enters via a color filter (a filter array) and impinges on a light-receiving face composed of a plurality of photodiodes (hereinafter referred to as xe2x80x9cpixelsxe2x80x9d or xe2x80x9clight detectorsxe2x80x9d).
The color filter types available comprise a primary color filter and a complementary color filter. A primary color filter is an array in which filters for the three primary colors, red (R) and green (G) and blue (B), are positioned at individual pixels in a predetermined order on the light receiving face. Similarly, a complementary color filter is an array in which color filers for four complementary colors, cyan (Cy), yellow (Ye), magenta (Mg) and green (G) are arranged in a predetermined order.
The processing performed in accordance with a signal obtained by the image pickup apparatus will now be described, while the color filer used for the apparatus is, for example, the above described complementary color filter.
First, a cyan filter absorbs red light within a visible radiation range, and a yellow filter absorbs blue light within a visible radiation range. Whereas while a magenta filter absorbs green light within a visible radiation range a green filter transmits only green light.
The arrangements used for these color filters will be described later.
The image pickup apparatus, wherein object light enters through the complementary color filter array, obtains a pixel signal Cy that corresponds to the volume of the light that strikes a pixel after passing through the cyan filter, a pixel signal Ye that corresponds to the volume of the light that strikes a pixel after passing through the yellow filter, a pixel signal Mg that corresponds to the volume of the light that strikes a pixel after passing through the magenta filter, and a pixel signal G that corresponds to the volume of the light that passes through the green filter.
The thus obtained pixel signals Cy, Ye, Mg and G are used, as luminance signal Y and color difference signals CB and CR, for adjusting the iris or the white balance for a digital still camera or for a detection process performed during auto focusing, or for an image pickup apparatus that performs compression or decompression processing.
The luminance signal Y and the color difference signals CB and CR are represented by the following equations (1) to (3), in which the pixel signals Cy, Ye, Mg and G are used.
Y=Ye+G+Cy+Mgxe2x80x83xe2x80x83(1)
CB=(G+Ye)xe2x88x92(Mg+Cy)xe2x80x83xe2x80x83(2)
CR=(Cy+G)xe2x88x92(Ye+Mg)xe2x80x83xe2x80x83(3)
In FIGS. 1 and 2 are shown example arrangement patterns for color filters in a complementary filter used for an image pickup apparatuses.
In the pattern shown in FIG. 1 for the complementary color filter, color filters are so arranged that they have a cyclic pattern of two pixels horizontally (the direction corresponding to that of C1, C2, C3, . . . ) and four pixels vertically (the direction corresponding to that of L1, L2, L3, . . . ). In the pattern shown in FIG. 2 for the complementary color filter, color filters are so arranged that they have a cyclic pattern of two pixels horizontally and eight pixels vertically.
With either complementary color filter, the luminance signal Y is obtained by performing the calculations for equation (1), for which are used the pixel signals Cy, Ye, Mg and G (shaded portions in FIGS. 23 and 24) for pixels in a four-pixel (2xc3x972) block including two pixels horizontally and two pixels vertically. Similarly, the color difference signals CB and CR can be obtained by performing the calculations for equations (2) and (3) that employ the pixel signals Cy, Y, Mg and G for pixels in a 2xc3x972 pixel block.
However, when a conventional image pickup apparatus, for which object light enters through the color filter shown in FIG. 1 or 2, is employed for a digital still camera, for example, the following problems have arisen.
(1) Before the shutter release is pressed, at the cost of resolution, a digital still camera reads pixel signals (in this case the above described image signals Cy, Ye, Mg and G) that are obtained by the image pickup apparatus (fast read mode), and based on these signals, displays images on the screen of a liquid crystal viewfinder or adjusts the iris or the white balance.
When the color filter shown in FIG. 2 is employed for an image pickup apparatus, image pixels obtained by the image pickup apparatus can be read in the fast read mode, and the white balance can be adjusted based on the signals. However, when the color filter shown in FIG. 1 is employed for an image pickup apparatus, and when for fast reading, at the cost of resolution, pixel signals for individual pixels are intermittently read vertically, only pixel signals Cy and Ye, i.e., pixel signals for only the two colors cyan and yellow, can be obtained, and the processing for white balance can not be employed.
(2) Recently, an image pickup apparatus, such as a CCD, has been provided wherein, by employing an elaborate signal reading method, object light is received at the light receiving face and pixel signals for two pixels that are perpendicularly adjacent to the light receiving face are added together, the resultant signal being transmitted to the transmission unit of the apparatus. As a result, the image pickup apparatus outputs paired pixel signals.
Specifically, when the color filter in FIG. 1 is employed for an image pickup apparatus, for lines L1 and L2 paired pixel signals Cy, for a pixel that is positioned at (C1, L1), and Mg, for a pixel that is positioned at (C1, L2), are output first, and then paired pixel signals Ye, for a pixel that is positioned at (C2, L1), and G, for a pixel that is positioned at (C2, L2), are output, the pixel signal pairs being sequentially output in the same way. And when the output of signals for lines L1 and L2 has been completed, for the succeeding lines L3 and L4 paired pixel signals Cy, for a pixel that is positioned at (C1, L3), and G, for a pixel that is positioned at (C1, L4), are output first, and then paired pixel signals Ye, for a pixel that is positioned at (C2, L3), and Mg, for a pixel that is positioned at (C2, L4), are output, the pixel signal pairs again being sequentially output in the same way, and the output of signals for the lines L3 and L4 is completed.
That is, the pixel signals output for lines L1 and L2 are (Cy+Mg), (Ye+G), . . . , and the pixel signals output for lines L3 and L4 are (Cy+G), (Ye+Mg), . . . .
However, since luminance signal Y and color difference signals CB and CR are acquired from the above output signals, there are signals that can not be used for the calculations performed using equations (2) and (3) to obtain color difference signals CB and CR.
That is, while equation (2) is set up using (G+Ye) and (Mg+Cy), the output signals for lines L3 and L4 are (Cy+G), (Ye+Mg), . . . , and as a result, the calculations for which equation (2) is used can not be performed for lines L3 and L4. Similarly, while equation (3) is set up using (Cy+G) and (Ye+Mg), the output signals for lines L1 and L2 are (Cy+Mg), (Ye+G), . . . , and as a result, the calculations for which equation (3) is used can not be performed for lines L1 and L2.
As is described above, a solution for equation (2) can be obtained for the outputs for lines L1 and L2, but no solution can be obtained for the outputs for lines L3 and L4. Likewise, a solution for equation (3) can be obtained for the outputs for lines L3 and L4, but no solution can be obtained for the outputs for lines L1 and L2.
Therefore, color signals CB and CR for the individual colors can be obtained only for the pixel signals for one line, although pixel signals are output for four lines by the image pickup apparatus. That is, since luminance signal Y and color signals CB and CR can not be obtained unless pixel signals for four lines are employed, accordingly, vertical resolution is reduced.
When the color filter shown in FIG. 2 is employed for the image pickup apparatus, pixel signal pairs are output in the same manner: pixel signal pairs of (Cy+Mg), (Ye+G), . . . for lines L1 and L2; pixel signal pairs of (Cy+Mg), (Ye+G), . . . for lines L3 and L4; pixel signal pairs of (Cy+G), (Ye+Mg), . . . for lines L5 and L6; and pixel signal pairs of (Cy+G), (Ye+Mg), . . . for lines L7 and L8.
However, since luminance signal Y and color signals CB and CR are acquired from the above output signals, there are signals for which equations (2) and (3), used to obtain color signals CB and CR, can not be solved.
That is, while equation (2) is set up using (G+Ye) and (Mg+Cy), the output signals for lines L5, L6, L7 and L8 are (Cy+G), (Ye+Mg), . . . As a result, a solution for equation (2) can not be obtained for these lines. Similarly, while equation (3) is set up using (Cy+G) and (Ye+Mg), the output signals for lines L1, L2, L3 and L4 are (Cy+Mg), (Ye+G), As a result, a solution for equation (3) can not be obtained for these lines.
As is described above, a solution for equation (2) can be obtained for the outputs for lines L1 to L4, but can not be obtained for the outputs for lines L5 to L8. Likewise, a solution for equation (3) can be obtained for the outputs for lines L5 to L8, but can not be obtained for the outputs for lines L1 to L4.
Therefore, color difference signals CB and CR for the individual colors can be obtained only for pixel signals for two lines, although pixel signals are output for eight lines by the image pickup apparatus. That is, since luminance signal Y and color difference signals CB and CR can not be obtained unless pixel signals for four lines are employed, accordingly, vertical resolution is reduced.
It is one objective of the present invention to generate an image signal that has a high resolution, both horizontally and vertically.
It is another objective of the present invention to efficiently acquire a color image signal having a high resolution.
It is an additional objective of the present invention to provide multiple modes, such as a mode for outputting a low-resolution image signal at a high speed and a mode for outputting a high-resolution image signal at a low speed, for an easy color display, for auto-focusing and for the automatic adjustment of the white balance.
To achieve the above objectives, according to one aspect of the present invention, an image pickup apparatus comprises:
a plurality of pixels arranged horizontally and vertically; and
a color filter array for four colors arranged in the plurality of pixels, wherein the color filter array has a cyclic pattern of four linesxc3x97four columns, and
wherein, in the cyclic pattern unit comprising four rows and four columns, colors of color filters on the same row differ from each other and colors of the color filters in the same column differ from each other.
According to one more aspect of the present invention, an image pickup apparatus comprises:
a plurality of pixels arranged horizontally and vertically; and
a color filter array of N colors (N is an integer) arranged in the plurality of pixels,
wherein the color filter array is so arranged that luminance signals are generated from all the rows and all the columns.
According to another aspect of the present invention, an image pickup apparatus comprises:
a plurality of pixels arranged horizontally and vertically; and
a color filter array of four colors arranged in the plurality of pixels, wherein the color filter array is so arranged that two color difference signals are generated by a cyclic pattern of two rows x two columns by using addition signals of pixels in the horizontal direction and by using addition signals of pixels in the vertical direction.
According to an additional aspect of the present invention, an image pickup apparatus comprises:
a plurality of pixels arranged horizontally and vertically;
a plurality of vertical output lines along which signals produced by the plurality of pixels are read;
a plurality of storage means, provided along the vertical output lines, for the storage of the signals produced by the plurality of pixels;
first addition means, provided along the vertical output lines, for adding together signals produced by pixels on the same row that are output by the plurality of storage means;
second addition means, provided along the vertical output lines, for adding together signals produced by pixels in the same column that are output by the plurality of storage means; and
a horizontal output line along which are read resultant signals produced by the first addition means and the second addition means.
According to a further aspect of the present invention, an image pickup apparatus comprises:
a plurality of pixels arranged horizontally and vertically; and
addition means for adding together pixels that are located adjacent to each other horizontally and/or vertically, while shifting the plurality of pixels by one pixel.
According to one further aspect of the present invention, an image pickup apparatus comprises:
a plurality of pixels arranged horizontally and vertically;
readout means for reading out signals produced by the plurality of pixels as a unit, comprising a pixel block that is composed of P linesxc3x97Q columns (P and Q are integers), while shifting the plurality of pixels horizontally or/and vertically by one pixel or predetermined number of pixels; and
saving means for saving signals produced in an area that overlaps the next pixel block that is shifted the predetermined number of pixels away from the pixel block in the area of the pixel block that is read by the readout means,
wherein the readout means employs the signals stored in the saving means to read a succeeding pixel block.
According to yet one more aspect of the present invention, a method for reading an image signal produced by an image pickup apparatus in which four color filters are disposed, comprises the step of:
calculating A+Bxe2x88x92Cxe2x88x92D for signals A, B, C and D produced by pixels at which are positioned the four color filters,
wherein pixels from which signals A and B are output are located adjacent to each other horizontally or vertically; and
wherein the color filters have a cyclic pattern of four rowsxc3x97four columns, and, in the cyclic pattern of four lines and four columns, colors of color filters on the same row differ from each other and colors of the color filters in the same column differ from each other.
According to yet another aspect of the present invention, a method for reading an image signal produced by an image pickup apparatus in which four color filters are disposed, comprises the step of:
calculating A+Bxe2x88x92Cxe2x88x92D for signals A, B, C and D produced by pixels at which are positioned the four color filters,
wherein pixels from which signals A and B are output are located adjacent to each other horizontally or vertically; and
wherein the color filters have a cyclic pattern of four rowsxc3x97four columns, and are so arranged that luminance signals are generated from all the rows and all the columns.
According to yet an additional aspect of the present invention, a method for reading an image signal produced by an image pickup apparatus in which four color filters are disposed, comprises the step of:
calculating A+Bxe2x88x92Cxe2x88x92D for signals A, B, C and D produced by pixels at which are positioned the four color filters,
wherein pixels by which signals A and B are output are located adjacent to each other horizontally or vertically; and
wherein the color filters are so arranged that two color difference signals are generated by a cyclic pattern of two rowsxc3x97two columns by using addition signals of pixels in the horizontal direction and by using addition signals of pixels in the vertical direction.
According to yet a further aspect of the present invention, an image processing system comprises:
an image pickup apparatus in which is mounted a color filter array for four colors;
a compressor for compressing data;
a decompressor for decompressing compressed data; and
a color processor for at the least performing an adjustment for white balance or for xcex3 correction,
wherein a signal from the image pickup apparatus is transmitted to the compressor without passing through the color processor, and a signal compressed by the compressor is decompressed by the decompressor, the resultant signal being transmitted to the color processor;
wherein the color filter array has a cyclic pattern of four rowsxc3x97four columns; and
wherein, in the cyclic pattern of four lines and four columns, colors of color filters on the same row differ from each other and colors of the color filters in the same column differ from each other.
According to yet one further aspect of the present invention, an image processing system comprises:
an image pickup apparatus in which is mounted a color filter array for N colors (N is an integer);
a compressor for compressing data;
a decompressor for decompressing compressed data; and
a color processor for at the least performing an adjustment for a white balance or for xcex3 correction,
wherein a signal from the image pickup apparatus is transmitted to the compressor without passing through the color processor, and a signal compressed by the compressor is decompressed by the decompressor, the resultant signal being transmitted to the color processor; and
wherein the color filter array is so arranged that luminance signals are generated from all the rows and all the columns.
According to still one more aspect of the present invention, an image processing system comprises:
an image pickup apparatus in which is mounted a color filter array for N colors (N is an integer);
a compressor for compressing data;
a decompressor for decompressing compressed data; and
a color processor for at the least performing an adjustment for white balance or for xcex3 correction,
wherein a signal from the image pickup apparatus is transmitted to the compressor without passing through the color processor, and a signal compressed by the compressor is decompressed by the decompressor, the resultant signal being transmitted to the color processor; and
wherein the color filter array is so arranged that two color difference signals are generated for a cyclic pattern of two rowsxc3x97two columns by using addition signals of pixels in the horizontal direction and by using addition signals of pixels in the vertical direction.
Other objectives and features of the present invention will become apparent during the course of the explanation given while referring to the following specifications and drawings.
With the above described arrangement, an image of high quality can be obtained.